The present invention relates to a resin cylinder head cover to which an oil control valve (OCV) is attached that controls supply and drainage of hydraulic pressure to and from a variable valve actuation mechanism of an internal combustion engine.
In a case where a hydraulically operated variable valve actuation mechanism is provided for a timing sprocket and a timing pulley of an internal combustion engine, hydraulic pressure supplying/draining oil passages from the oil control valve to the variable valve actuation mechanism are formed in a camshaft.
As described above, since hydraulic pressure needs to be supplied to one of the oil passages formed in the camshaft, a configuration has been proposed in which an oil control valve is attached to the inner surface of the cylinder head cover, and the hydraulic pressure is supplied to the oil passage in the camshaft from the oil control valve via an oil passage formed in a cam cap.
However, according to the configuration in which the oil control valve is accommodated inside the cylinder head cover as described above, the height of the cylinder head cover is increased by a space necessary for accommodating the oil control valve. This undesirably increases the size of the internal combustion engine. Therefore, a technique has been proposed in which an oil control valve is accommodated in a valve case attached to the cylinder head cover to cover an opening formed in the upper wall of the cylinder head cover (for example, see Japanese Patent No. 3525709).
With this configuration, since the distance between the oil control valve and the cam cap is increased, an intermediate member, which has oil passages for connecting the oil passages in the oil control valve to the oil passages in the cam cap, is additionally arranged between the oil control valve and the cam cap. In this case, the hydraulic pressure supplying/draining oil passages extending from the oil control valve to the variable valve actuation mechanism is formed by the valve case, the intermediate member, the cam cap, and the camshaft.
However, according to the configuration of Japanese Patent No. 3525709, a large number of components are employed. Moreover, since metal machining needs to be performed, the valve case and the intermediate member need to be machined with high precision as well as the oil control valve. In particular, since the attachment between the valve case and the intermediate member and between the valve case and the oil control valve must be oil-tight, the valve case needs to be machined with high precision at least at two attaching portions. Furthermore, since the single valve case is machined at two attaching portions, the machining process on each attaching portion may cause the other attaching portion to be deformed due to cutting resistance. Therefore, the attaching accuracy of the oil control valve including the intermediate member may be decreased. Moreover, since high precision metal processing is executed many times within a narrow range, foreign object such as chips is likely to remain on the valve case.
If the cylinder head cover and the valve case configured as described above are formed with resin to achieve the weight reduction, foreign object such as chips will not remain. However, when attaching the cylinder head cover to a cylinder head, the cylinder head cover may be deformed since the rigidity of resin is relatively low. This may, in turn, affect the valve case. In this case, although the two attaching portions are machined with high precision, the dimensional accuracy of the attaching portions may be decreased and the oil control valve may not be properly attached to the valve case due to the deformation caused when attaching the cylinder head cover to the cylinder head.